1. Field of the Invention
The present invention is related to the field of vehicle suspensions and drivetrains. More specifically, the invention relates to semi-independent suspensions and drivetrains for vehicles.
2. Description of Related Art
Numerous designs for suspension and drivetrain systems are known and used in the manufacturing of various types of vehicles. It is known in vehicle engineering that particular designs provide specific advantages in particular applications. Most of the developments in the designing of suspension and drivetrain systems have been centered around automotive applications.
In recent times, smaller specialized all-terrain vehicles (a.k.a. ATVs) have gained in popularity as recreational and utility vehicles. As the popularity of ATVs has increases, so to have the performance demands placed upon them. Consequently, manufacturers of ATVs have responded with performance increases in certain areas, such as, increases in engine power and vehicle size. Such increases in engine output and vehicle size translate into increased inertial effects and extreme dynamic loading. These more powerful, massive ATVs usually require more skill and/or effort by the operator to maintain control during operation. However, ATV manufacturers have had very little success in modifying the previously mentioned automotive suspension and drivetrain designs to optimally adapt them for ATV use.
ATVs require the development of specialized suspension and drivetrain systems to improve operator controllability while continuing to withstand the rugged demands of their off-road application. Typically, ATVs have one or two front wheels and two rear wheels axially mounted on a solid axle in a dependent manner by a swing arm that pivots about a transverse axis of the ATV. Such a system is illustrated in U.S. Pat. No. 4,582,157 to Watanabe. The limitation and disadvantage of this suspension and drivetrain design is that the two rear wheels are mounted on a solid axle, which is axially coupled to a swing arm in such a way that it is only allowed to pivot about, and constrained to be parallel with, the transverse axis of the ATV.
Currently, the three and four wheeled ATVs using the ""157""s design, yield three undesirable characteristics that have negative effects on vehicle stability. The first two of these undesirable characteristics are in effect during both forward and turning or cornering operations of the ATV. These two characteristics are termed in vehicle engineering as suspensions having a roll center at ground level and possessing infinite roll resistance.
Having the roll center at ground level results in poor roll stability because the center of gravity (a.k.a. CG) of the vehicle can only be designed far above the vehicle""s longitudinally oriented roll axis, potentially resulting in increased dynamic roll moment (a.k.a. torque). Infinite roll resistance implies that the suspension doesn""t incorporate any roll motions to absorb roll energies. This means that all of the energy that is transferred via the unsprung mass (a.k.a. unsprung weight) from dynamic roll loading, is transferred directly into rolling the sprung mass (a.k.a. sprung weight) of the vehicle. Thus, infinite roll resistance translates into a harsh ATV dynamic roll response that is often difficult to predict and control by the operator. Even during simple forward motion, operating such an ATV can be like riding a twisting, bucking bronco when traversing uneven off-road terrain.
The third undesirable characteristic comes into play when the solid axle drivetrain of the ""157 patent is used and the operator is attempting to negotiate the ATV to turn or corner. For the operator to negotiate the ATV around a turn, a sufficient turning moment must be generated by the operator to overcome all resistive turning moments. Usually, these resistive turning moments are primarily caused by inertial effects, which are overcome by the operator simply turning the front steering mechanism of the ATV. This steering action imparts the needed centripetal reaction from the front tires to overcome the inertial turning moments that work to maintain forward motion of the ATV.
This third undesirable characteristic, which is imparted due to the solid axle constraining the rear wheels to rotate at the same speed, is a mechanical counteracting turning moment, and it""s contribution is only present while both rear tires are in sufficient traction with the terrain. This mechanical counteracting turning moment causes the ATV to experience a condition termed as understeer. For the operator to better negotiate this ATV to turn, one must overcome this understeer effect. This is typically accomplished by the operator leaning outward to shift the CG of the sprung mass such that a sufficient roll moment is imparted to cause the inside rear tire to lose traction with the terrain, thereby decoupling the mechanical counteracting turning moment caused by the solid axle. Thus, the operator must perilously put the ATV in an unsafe and unstable inertia induced roll condition in order to eliminate or reduce the mechanically induced understeer effect.
The sudden removal of this counteracting turning moment results in a nearly instantaneous transition from a quasi-static understeer condition to a sharp oversteer condition. This oversteer works to worsen the preexisting unstable inertia induced roll condition. Depending on the skill and strength of the operator, this situation can result in a rapid loss of operator roll control and vehicle rollover.
In light of the disadvantages inherent in the above suspension and drivetrain system, it has been recognized that significantly improved vehicle roll dynamics could be obtained if the rear suspension was designed such that the rear axle could also pivot about the vehicle""s longitudinally oriented roll axis. These types of semi-independent suspensions offer variably finite roll resistance characteristics which are desirable for increased roll stability and traction.
The most important function of any suspension is to keep the tires in contact with the ground, while maximizing stability. Semi-independent rear suspension motion is all that is necessary for off-road ATV applications because the tires used are of low pressure, and they have rounded shoulders with radical tread patterns extending well into the sidewall region. These tire characteristics nullify the need of having a fully independent suspensions because the tires provide good compliance and traction with the terrain, even if the motion of one side of the suspension moderately affects the other.
In this regard, U.S. Pat. No. 5,845,918 to Grinde et al. discloses an ATV with a semi-independent rear suspension which allows the rear axle to pivot about the vehicle""s longitudinal centerline as well as about a transverse axis. This suspension design has been found to substantially improve handling performance of the ATV by giving improved traction on uneven terrain and increased vehicle roll stability. In particular, during cornering, these semi-independent suspensions help roll stability because they postpone the initiation of the transition from understeer to oversteer. For the operator, a quasi-static understeer condition is easier to control than the rapid transition condition to a sharp oversteer.
The suspension system of the ""918 patent however, does not totally resolve the third undesirable characteristic explained above, since it too uses a solid rear axle. In addition, the suspension design of the ""918 patent severely limits the travel of the rear axle since the travel is limited by the travel of the coil-over shocks, which are displaced in near one to one ratio with the displacement of the rear axle. Thus, the suspension disclosed in the ""918 patent is undesirable for ATV applications, especially for high performance applications, where amount of travel in a suspension is considered critical for optimal traction, energy absorption, and operator control.
Furthermore, the drivetrain of the ""918 patent is like the other prior art suspension and drivetrain systems which typically utilize a drive shaft with a final drive bevel gear which are housed in a shaft housing and a final drive housing. As can be easily appreciated, these components are all made of metal and are quite massive thereby adding to the unsprung mass of the ATV.
Increased mass translates into power robbing inertial drivetrain losses, poor suspension response, and decreased overall power to mass (a.k.a, power to weight) ratio, which is very critical in high performance racing applications where maximum acceleration is imperative. More specifically, it is important to minimize the unsprung mass so that wheel hop frequencies are much higher than the sprung mass natural frequencies. This helps to ensure that the sprung mass remains relatively stable during wheel hop. Thus, a lesser unsprung mass provides superior suspension response and vehicle handling characteristics.
Lastly, because of the bulkiness of the suspension components and the presence of the drive shaft housing and the final drive housing in the prior art designs, there is no effective manner for providing a cost effective precision braking system for the rear wheels. In particular, it is well recognized that disk brake systems are especially desirable in high performance applications. Generally, disk brake systems provide more precise braking control than drum brake systems and are less massive, thus again, minimizing the unsprung mass and drivetrain inertial effects.
However, because the drive shaft housing and the final drive housing are generally positioned substantially center of the rear axle in a conventional ATV, they pose severe packaging constraints for a disk braking system. Thus, many ATVs incorporate the easier to package, yet less precise and more massive drum brakes at the outward ends of the axle housing, the only place possible for robust braking. Having these added braking masses outward from the central region of the axle further worsens the unsprung mass dynamic roll response by increasing the unsprung mass radius of gyration (a.k.a. polar moment of inertia).
One method of reducing the unsprung mass and reduce the bulkiness of the drivetrain is to utilize a chain and sprocket drive coupling such as those used in motorcycles, where they have proven to be superior to all other methods of drivetrain coupling for off-road applications. Chains and sprockets are less massive as compared to drive shafts and final drive bevel gears, and they provide a very responsive coupling of the drive wheels to the transmission. They also take up only minimal amount of space and impose only minimal packaging constraints for a disk braking system. Further, flexible couplings, including chains, absorb drivetrain shock, in the form of strain energy, providing a smoother coupling than that provided by shaft and gear drivetrain systems which often induce shock themselves because of gear lash issues.
However, the use of a conventional chain and sprocket drive system does not allow the rear axle to pivot about the vehicle""s longitudinally oriented roll axis, for these chain couplings require that their elements remain planar. These conventional chain drive system typically incorporate a drive sprocket which is attached to the transmission and is in a fixed orientation, and a driven sprocket which spins about the drive axis and is constrained to pivot about, and remain parallel to, the rear transverse axis.
In other applications, special sprockets have been designed to allow the use of a chain and sprocket drivetrain while providing some amount of roll movement. Such drive sprockets are illustrated in U.S. Pat. No. 4,469,188 to Mita which is directed to an articulated tricycle including a drivetrain with a drive sprocket located about a shaft with a constant velocity universal joint employed to allow some flexibility between the sprocket and the shaft. The driven sprocket of the ""188 patent is coupled to the solid rear axle by a chain for driving the rear wheels such that the front body of the tricycle may roll slightly relative to a rear body of the tricycle. However, application of the chain and sprocket drivetrain of the ""188 patent has been found to be very difficult and inadequate in applications where large suspension travel and low unsprung mass are desired such as in an ATV application. The rear wheels of the ""188 patent are supported primarily through the constant velocity universal joint housing and is inadequately supported for off road use. Furthermore, relative to the embodiment being discussed, the ""188 patent, again, does not totally resolve the third undesirable characteristic explained above, since it too uses a solid rear axle, albeit because the two rear wheels are so close together and are so small, the resistance will be smaller than the other aforementioned prior art. Moreover, there are no easy ways to provide for the superior characteristics of a disk braking system.
U.S. Pat. No. 4,877,102 to Stewart discloses a multi-wheeled vehicle suspension and drive mechanism for ATVs including a rear axle assembly which allows the rear axle to roll. The ""102 patent also discloses a sprocket and chain drive system including a driven sprocket with a universal joint which is mounted to the axle and aligned with the drive sprocket by a pivot arm which is mounted to the swing arm. Whereas the suspension and drive mechanism of the ""102 patent allowed larger suspension travel and roll than the design of the ""188 patent, the design disclosed in the ""102 patent is complicated, requiring many numerous components. In particular, because the design disclosed in the ""102 patent includes an axle housing and its associated components, which are all quite massive, and they counteract some of the benefits of using a chain drive in the first place since all of these additional components act to increase unsprung mass. In addition, because of the complexity, the design disclosed in the ""102 patent is cost prohibitive to manufacture. Furthermore, because of the relative complexity of the system, it has been found to be unreliable, especially since dirt and debris tended to accumulate in the various components of the universal joint as well as the other exposed components. Lastly, it still fails to resolve the third undesirable characteristic explained above, since it too uses a solid rear axle. Consequently, this suspension and drive mechanism has not been readily accepted and is not commonly used.
Thus, despite the many disadvantages and limitations of commonly used ATV suspensions and drivetrains, they remain in use because there have yet to be any known practical alternatives which will practically avoid the aforementioned undesirable characteristics. Further, these commonly used rear suspension and drivetrain systems are accepted because some offer the required large range of suspension travel needed for added ground clearance and energy absorption. They are simple, tough, and packaged to minimize effects of collision with ground debris.
There are many other suspension and drive designs that could offer improved roll stability characteristics but at the expense of decreased suspension travel, reduced available ground clearance, and less energy absorption ability. These on-road, automotive type suspension systems are optimally suited for street applications where flat faced lower profile tires are used. Further, these designs are more complex, massive, and require packaging that is more vulnerable to collision with ground debris.
For the foregoing reasons, there exists an unfulfilled need for an improved semi-independent suspension and drivetrain system for vehicles which will enable improved roll and traction performance by allowing the axle to pivot about a vehicle""s longitudinally oriented roll axis as well as a transverse axis. In addition, there exists an unfulfilled need for such a suspension and drivetrain system which will allow extensive range of suspension travel. Furthermore, there exists an unfulfilled need for such a suspension and drivetrain which will minimize the resistive turning moments associated with the usage of a solid rear axle. Still further, there exists an unfulfilled need for such a suspension and drivetrain which will enable the use of a, proven to be superior, flexible coupling drivetrain, such as a flexible chain coupling drivetrain, including a drive sprocket and a driven sprocket. Moreover, there exists an unfulfilled need for such a suspension and drivetrain which will attain the above objectives and include provisions for a disk brake system. Lastly, there exists an unfulfilled need for such a suspension and drivetrain which is simple, compact, robust, and cost effective.
In view of the foregoing, one advantage of the present invention is in providing an improved semi-independent suspension and drivetrain system for vehicles which will enable improved roll and traction performance by allowing the axle to pivot about a vehicle""s longitudinally oriented roll axis as well as the transverse axis.
Another advantage of the present invention is in providing such an improved suspension which will allow extensive range of suspension travel.
A third advantage of the present invention is in providing such an improved suspension and drivetrain system which will minimize the resistive turning moments associated with the usage of a solid rear axle.
A fourth advantage of the present invention is in providing an improved suspension and drivetrain system which will minimize the unsprung mass of the vehicle.
A fifth advantage of the present invention is in providing such an improved suspension and drivetrain system enabling the use of a flexible coupling drivetrain, such as a flexible chain coupling drivetrain, including a drive sprocket and a driven sprocket.
A sixth advantage of the present invention is in providing an improved suspension and drivetrain system which will attain the above objectives and include optimal provisions for a disk brake system.
A seventh advantage of the present invention is in providing such an improved suspension and drivetrain system which is simple, compact, robust, and cost effective.
In accordance with preferred embodiments of the present invention, an integrated semi-independent suspension and drivetrain system for a vehicle is providing including a swing arm with a swing mount for pivotally mounting the swing arm to the vehicle, an axle assembly rotatable along a transverse axle rotation axis, an axle carrier for mounting the axle assembly, the axle carrier being rotatably mounted to the swing arm to allow the axle assembly to roll about a suspension roll axis, a driven sprocket substantially centrally attached to the axle assembly for rotating the axle assembly, a drive sprocket for transferring rotational power to the driven sprocket, a flexible coupling mechanically linking the driven sprocket to the drive sprocket to allow transfer of rotational power from the drive sprocket to the driven sprocket, a roll movement means for allowing the flexible coupling to maintain the mechanical link between the driven sprocket and the drive sprocket as the driven sprocket rolls about the suspension roll axis with the axle carrier, and at least two shock mounts, each for mounting a shock absorber or a spring, the two shock mounts being positioned along sides of the axle carrier flanking the suspension roll axis on two sides at a spaced distance away from the suspension roll axis.
In accordance with one embodiment of the present invention, the swing arm and the axle carrier are substantially tubular in shape and the axle carrier is dimensioned to be rotatably mounted to the swing arm, with at least one bearing mounted between the axle carrier and the swing arm to reduce friction between the axle carrier and the swing arm. The swing arm may include one swing mount which is attached to the swing arm by at least one of a lateral reinforcement rib and a laterally inclined reinforcement rib which may also include a perpendicularly oriented reinforcement rib. The axle carrier and/or the swing arm may include an internal reinforcement web extending substantially therethrough.
In accordance with another embodiment, the integrated semi-independent suspension and drivetrain system includes an extensible adjustment mechanism adapted allow adjustment of axial position and preload of the axle carrier relative to the swing arm. In this regard, the adjustment mechanism may include an adjustable axle carrier-to-swing arm bearing constraint on the axle carrier and/or the swing arm. The bearing constraint mechanism may include a preloading wave ring, a retaining ring, a shim ring, and/or a bearing adapter ring. In yet another embodiment, the axle carrier includes a rotatable adjustment mechanism to allow adjustment of radial position of the axle assembly relative to the axle carrier. The rotatable adjustment mechanism preferably includes at least one radial eccentric bearing constraint.
The flexible coupling may be a drive chain or a flexible belt and the axle carrier may include a tensioner for reducing slack in the flexible coupling, the tensioner preferably engages a lower portion of the flexible coupling. The roll movement means includes a movable joint centrally disposed on the drive sprocket to allow alignment of the drive sprocket relative to the driven sprocket. In this regard, the movable joint may be a constant velocity (CV) joint, a universal joint (U-Joint), and/or a curvic spline joint (CSJ). In this regard, a guide adapted to align the drive sprocket with the driven sprocket may also be provided, the guide being provided on a guide mount which extends from the axle carrier to the drive sprocket. The guide may be a cutaway provided on an edge of the guide mount or include a thrust bearing and/or a roller mounted on the guide mount.
In accordance with another embodiment of the present invention, the integrated semi-independent suspension and drivetrain system may further include an axle bearing that supports the axle assembly and a bearing preload adjuster adapted to allow adjustment of relative axle bearing preload between the axle assembly and the axle carrier. In this regard, the bearing preload adjuster may include an adjustable axle bearing constraint on at least one of a left axle, a right axle, and the axle carrier where the adjustable axle bearing constraint includes at least one of an eccentric bearing constraint, a preloading wave ring, a shim ring, and a retaining ring.
In accordance with yet another embodiment of the present invention, the axle assembly includes a left axle and a right axle and the driven sprocket includes a differential gear system to allow the left axle to rotate at a different rotational speed compared to the right axle. The differential gear system preferably comprises a plurality of pinion gears, at least one of the left axle and the right axle includes a sun gear at one end for engaging the plurality of pinion gears and at least one of the left axle and the right axle includes a ring gear at one end for engaging the plurality of pinion gears. The driven sprocket preferably includes at least one pinion constraint member at a hub of the driven sprocket for retaining the pinion gears and the pinion gears are caged between the sun gear and the ring gear. In this regard, the pinion gears rotate on axes that remain parallel to the transverse axle rotation axis. The left axle and the right axle are preferably supported relative to one another in an inter-cantilevered manner where a portion of one of the left axle and the right axle is received in, and mutually supported by other of the left axle and the right axle, further including at least one bearing therein between.
In accordance with still another embodiment of the present invention, the integrated semi-independent suspension and drivetrain system further including a brake assembly for exerting a braking force on the driven sprocket to resist rotation of the driven sprocket. In this regard, the driven sprocket includes a brake surface, and the brake assembly includes a brake caliper with brake pads for frictionally engaging the brake surface of the driven sprocket. The brake caliper may be mounted on the axle carrier or may be a floating brake caliper. In one preferred embodiment, the driven sprocket includes at least one of an axially extending flanges and radially extending flanges adjacent to the flexible coupling around a periphery of the driven sprocket. In such an embodiment, the driven sprocket includes an axially extending flange, a radial dimension of the axially extending flange being smaller than a radial dimension of a plurality of teeth on the driven sprocket, while the radial dimension of the radially extending flanges is at least equal to a radial dimension of a plurality of teeth on the driven sprocket.
In addition, or alternatively, the brake assembly includes a left brake disk disposed on a left side of the driven sprocket and is adapted to frictionally engage a left side of the driven sprocket, and a right brake disk disposed on a right side of the driven sprocket and is adapted to frictionally engage a right side of the driven sprocket, the left brake disk and the right brake disk preferably being rotationally fixed relative to the axle assembly. In this regard, the left brake disk and the right brake disk are floating disks and the caliper is a floating caliper. The driven sprocket may also include a friction material that frictionally engage the left brake disk and the right brake disk. For instance, floating friction disk disposed between the left brake disk and the driven sprocket and another floating friction disk disposed between the right brake disk and the driven sprocket may be provided. Alternatively, the left brake disk and the right brake disk each include a friction material on an inner surface for frictionally engaging the driven sprocket.
The integrated semi-independent suspension and drivetrain system in accordance with yet another embodiment of the present invention may also include a peripheral opening on a peripheral surface of at least one of the swing arm and the axle carrier to allow at least a segment of the flexible coupling extending between the driven sprocket and the drive sprocket to be outside of at least one of the swing arm and the axle carrier. In this regard, the peripheral opening may preferably be dimensioned in a manner that a clearance space exists between the flexible coupling and the peripheral opening throughout a range of motion of the flexible coupling, the range of motion being defined by rotation of the axle carrier and alignment of the drive sprocket with the driven sprocket.
In accordance with still another embodiment, the present invention provides an integrated semi-independent suspension and drivetrain system for a vehicle where the transverse axle rotation axis of the axle assembly is elevated above the suspension roll axis. The swing arm and the axle carrier may be substantially tubular in shape and the axle carrier may be dimensioned to be rotatably mounted to the swing arm, while the axle carrier includes two axle mounting flanges for mounting the axle assembly, the driven sprocket being positioned thereinbetween. The axle carrier may include at least one shock mount for mounting at least one of a shock absorber and a spring which is positioned substantially along a midportion of the axle carrier at a spaced distance away from the suspension roll axis. Preferably, the two shock mounts are provided which are positioned flanking the suspension roll axis on two sides at a spaced distance from the suspension roll axis so that when springs are mounted to the two shock mounts, the springs resist roll rotation of the axle carrier relative to at least one of the swing arm and the vehicle.
The integrated semi-independent suspension and drivetrain system may further including a stabilizer bar for establishing a mechanical linkage between the axle carrier and at least one of the swing arm and the vehicle in a manner to resist roll rotation of the axle carrier relative to at least one of the swing arm and the vehicle. A damper to dampen rotation of the axle carrier relative to the swing arm may also be provided.
These and other objects, features and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments of the invention when viewed in conjunction with the accompanying drawings.